This invention is a spring shoe called herein a space shoe. Its sole is a structure constrained to compress without tilting; this structure is called herein the p-diamond. This optimally simple, anti-tilt, compressible structure comprises overlapping diamond and parallelogram linkages which constrain an upper plate from tilting as it moves vertically up and down with respect to a lower plate. The p-diamond has many applications where non-tilt spring systems are required, and it is an inexpensive alternative to telescopically guided spring systems. P-diamond applications include, but are not limited to, the space shoe, which also has a push-off means to allow natural foot action.
The first embodiment of the space shoe is called herein a space shoe because most of the skeletal sole is free space rather than a solid, foam-filled structure. The springs of the space shoe act directly between the ground plate and the shoe plate; that is, these springs are located at shoe or sole level. The second embodiment of the invention is called a bow shoe; its bow spring is located at the shin level, or above, to minimize the device weight at foot level.
The space shoe provides for the following improvements (referred to as S1-S3 with xe2x80x9cSxe2x80x9d for space shoe). (S1) It has an improved mechanism to capture both heel and toe impact energy and return all impact energy through the toe during the latter part of toe-off. (S2) It provides for optimal stability by constraining an upper shoe plate to not tilt with respect to a lower ground platexe2x80x94via a linkage called herein a p-diamond linkage. Improvement (S2) is referred to herein as sole tilting. Improvement (S3) is that a natural running action is allowedxe2x80x94where this running action comprises both a natural roll-over from heel to toe and a push-offxe2x80x94with the wearer""s metatarsal joint freely flexing and the heel lifting into the air during toe-off.
Seven categories of prior shoe art with springs or relevant features are listed below. Examples of each category will be given, along with limitations overcome by the space shoe improvements which improvements will be referred to by the numbers S1 to S3 mentioned above. The first category has multiple springs located throughout the sole or only in the heel. Examples include U.S. Pat. No. 5,621,984 of Hsieh and U.S. Pat. No. 5,337,492 of Anderie. Space-shoe improvements S1, S2, and S3 apply to this category which prior art notably permits sole tilting (S3) and dissipates heel impact energy in mid-stance (S1). With regard to improvement (S1), as the wearer""s heel lifts to push-off, the prior-art heel springs release their energy prematurely, the wearer""s knee bends and his ankle dorsi-flexes during which time the heel impact energy is largely dissipated. In fact, for this heel impact energy to efficiently propel the wearer up and forward, it must act through the wearer""s toe during the latter part of toe-off.
The second category of xe2x80x9csprings in solesxe2x80x9d prior art has a means to captures all of the heel impact energy for energy return at toe-off. An example is U.S. Pat. No. 4,936,03 of Rennex. Improvements (S2 and S3) apply, and the space-shoe mechanism to achieve improvement (S1) is considerably simpler and cheaper. The third category of xe2x80x9csprings in solesxe2x80x9d prior art has a linkage to constrain a compressible sole as a spring stores impact energy. Examples include U.S. Pat. No. 4,534,124 of Schnell, U.S. Pat. No. 5,896,679 of Baldwin, U.S. Pat. No. 5,701,685 of Pezza. Space-shoe improvements (S2 and S3) apply to Schnell and Pezza. Improvements (S1, S2, and S3) apply to Baldwin.
A third category of relevant prior art does not actually have springs in the soles. Rather, these patents do provide means for the wearer to flex their metatarsal joint and push off their toe. U.S. Pat. No. 4,400,894 of Erlich, U.S. Pat. No. 5,926,975 of Goodman, and U.S. Pat. No. 5,384,973 of Lyden all feature a narrowing of a conventional, solid sole under the metatarsal joint, and there are many other examples of this solution. U.S. Pat. No. 6,079,126 of Olszewski uses the just-mentioned xe2x80x9cnarrowingxe2x80x9d solution as well as another solution where a conventional, solid sole is split and the upper section lifts with the wearer""s heel. A U.S. Pat. No. 5,282,325 of Beyl also teaches a split sole with a torsion spring in the heel.
The current patent also provides for the wearer to flex his metatarsal joint and push off his toexe2x80x94in a variety of ways. However, the sole structure of the space shoe is distinctxe2x80x94in that it comprises a linkage between plates, instead of the conventional, solid sole of the just-mentioned prior art. That is, even though the xe2x80x9ctoe-flexxe2x80x9d function is the same, the structure and designs of the current patent are quite different and novel, and the general idea of a means for toe-flexing is old in the art.
With reference to the second embodiment of the invention, namely the bow shoe, the above improvements (S1, S2, and S3) still applyxe2x80x94along with some additional improvements labeled xe2x80x9cBxe2x80x9d for bow shoe. (B1) The bow shoe minimizes weight at the foot for improved energy efficiency. (B2) It uses bow springs to achieve a constant force curve. (B3) It permits optimally few, long, and light bow springs. (B4) It provides for optimal stability by minimizing the unweighted sole thickness.
The fourth category of xe2x80x9csprings in solesxe2x80x9d prior art has a spring and suspension mechanism in the heel. An example is U.S. Pat. No. 6,115,942 of Paradis with a bow spring. Improvements (S1, S2, B3, and B4) apply to this patent. Another example is U.S. Pat. No. 6,131,309 of Walsh with improvements (S1-S3 and B1, B3 and B4) applicable. The fifth category has a curved ground support hingeably connected in front and in back to the shoe and a single spring in the center. An example is UK Patent # GB2,179,235 of Waldron. Improvements (S1-S3 and B1-B4) apply to this category. The sixth category of has a linkage to constrain a compressible sole as a spring stores impact energy. Examples include U.S. Pat. No. 4,534,124 of Schnell, U.S. Pat. No. 5,896,679 of Baldwin, U.S. Pat. No. 5,701,685 of Pezza. Improvements (S2, S3 and B1-B4) apply to Schnell and Pezza. Improvements (S1-S3 and B1-B4) apply to Baldwin. The seventh and final category uses a linkage to connect the toe of a shoe to the mid-section of a bow spring, the bottom of which contacts the ground. A commercial product of ALANSportartikel, address: GmbH Grafratherstrasse 53, 82288 Kottgeisering/Germany, marketed under the brand name of xe2x80x9cPowerskipxe2x80x9d and referenced by their website, http://www.powerskip.de, is the only example of this category. Improvement (S3) applies because the force curve is not as constant as for an axially-loaded bow spring, and improvements B3 and B4 apply. The most notable improvement is (B2) because the foot of the wearer of xe2x80x9cPowerskipxe2x80x9d is a substantial distance above the ground even when the bow spring is fully compressed.
With reference to the space shoe, in both space shoe and bow-shoe embodiments, the key feature is a compressible sole comprising an eight-bar linkage (called herein a p-diamond sole) which constrains the upper shoe plate not to tilt as it moves vertically up and down with respect to the ground plate. Another feature is a push-off means which allows the wearer to freely push off her toe. Another feature is that a minimal number of springs and stops (even one) of any kind can be used (without need of a spring guide). In one embodiment, the spring system assists heel lift in the latter part of toe-off, thereby reducing the muscle energy expenditure of the calf muscles. These springs and stops can easily be replaced to fit the performance requirements of an individual for walking and running. Another feature is a heel hugger mechanism which ensures that the entire rear section of the space shoe xe2x80x9chugsxe2x80x9d the heel of the wears during swing phase. Another feature is a back-flexing outrigger, called herein a xe2x80x9cflex-rigger,xe2x80x9d to prevent sprained ankles; the flex-rigger can be used not only with the space shoes, but also as a retrofit or an integral part of conventional shoes or boots. Another feature is a curved extension extending backward from the bottom of the sole heel; this is called herein a xe2x80x9cback-heel.xe2x80x9d The back-heel minimizes the deceleration of the user""s center of mass at heel-strike by reducing the effective angle (backward, off-vertical) of the leg support. The back-heel can also as a retrofit or an integral part of conventional shoes or boots.
The advantages of the space shoe include: the sole can be very thick (2-6 inches) thereby make a wearer taller and enhancing her stride; even when the sole is thick, the wearer""s foot rolls over from heel to toe naturally; the wearer pushes off naturally; the shoe is energy-efficient in that it returns maximum impact energy (due to both heel impact and toe impact) to the wearer during thrust at toe-off when it is best utilized; the shoe is light-weight and cheap to manufacture; there are spring systems which provide for a constant force curve, instead of a linear force curve, thereby permitting faster running for a given maximum force, thereby reducing impact injuries; since the surface in contact with the foot is very thin, it is easy to ventilate the foot; this foot-contact can be shaped as a foot orthotic; and the sole thickness (1xe2x80x3 to xe2x89xa66xe2x80x3) and area can easily be changed due to the modular construction.
A critical insight motivating the p-diamond sole is that, in order for heel impact energy to efficiently propel the runner up and forward, it must act through the runner""s toe during the latter part of toe-off. The p-diamond sole prevents tilting of the compressible sole, and this constraint causes the heel impact energy to be returned at toe-off. Another performance enhancement in terms of energy efficiency results from the fact that the p-diamond sole can be made very thick. This allows the wearer to minimize knee flexion in both walking and running.
With reference to the bow-shoe embodiment only, one key feature is a bow spring to achieve a constant spring force curve which doubles the potential energy storage in a sole of a given thickness. Another key feature is a suspension system in which a bow spring is loaded by full foot impactxe2x80x94both by the heel and the toe. This suspension system permits the location the bow spring above the foot at the shin or thigh level to minimize the device weight at foot levelxe2x80x94thereby improving energy efficiency. Also, the use of an 8-link system allows the sole components to be optimally light. Another improvement is related to the constant force curve, referred to as a buckling curve, achievable with bow springs. This allows a safe threshold force level to be set, and twice as much energy call be stored for a given sole thickness as with a linear spring. Also, bow springs can be more than 90% energy efficient. A consequence of the anti-tilt feature inherent in the p-diamond sole is that a spring located anywhere in the sole resists sole compression at both the toe section and the heel section. This means that one or two springs or stops suffice, and modular design makes it a simple matter to change springs to tune the bow shoe to an individual""s weight and gait and to change shoe and ground plates for different size feet. Another improvement is that the bow shoe provides for optimal stability by minimizing the unweighted sole thicknessxe2x80x94by virtue of the remote location of the bow spring above the foot level. That is, since the bow springs are not located in the sole, the sole can be fully compressed. Finally, the p-diamond sole can be manufactured very cheaply.
Other applications of the main invention, the p-diamond include 1) a spring/foot component of a walking/running brace or of a backpack-supporting brace for walking and running and 2) xe2x80x9cone degree of motionxe2x80x9d actuators for prostheses or for robotics.